I'm afraid I can't offer a solution just loads of sympathy. Our dd is 21 months and has done this on and off for a couple of months. She is cutting a molar but I don't think that is really the cause. She is just developing a strong personality and is enjoying pushing things a bit more. Her latest is to remove sleepsuit and nappy and yell for attention.
However when we are out she is if anything becoming more clingy and panicking if I go out of her immediate view to the point of hysteria. She has had a tendency to cry and be anxious when left since she was 5 months old but this is different, both more disturbing and exhausting.
Does your ds settle himself for naps in the daytime. Is he perhaps not really tired, or otherwise may be overtired, at 7 (dd's bedtime has drifted from 7 towards 7.30-8 pm in recent weeks).
Anyway I hope you solve your ds's sleep issues, and hope someone can post some ideas which would help us too.